In general, so-called RF tags including IC chips, in which predetermined information on articles and objects is readably and writably stored, are broadly used to the various articles and objects.
The RF tag is also called an RFID (Radio Frequency Identification) tag, an IC tag, a non-contact tag or the like. The RF tag is a microminiature communication terminal, which is obtained by shaping, in the form of a tag (baggage tag), a so-called inlay (inlet) where an electronic circuit including an IC chip and a radio antenna is sealed or coated with a substrate such as a resin film. In the RF tag, reading-only the predetermined information from the IC chip, writing-once it in the IC chip, and reading it therefrom and writing it therein are possible by a reader/writer via radio.
Furthermore, when the predetermined information is written in such an RF tag and the thus treated RF tag is then attached to, e.g., each of various articles or objects, the information recorded in the RF tag is picked up by the reader/writer, to enable recognition, output, display, update and the like of the information recorded in the tag as the predetermined information on the articles.
In such an RF tag, several hundred bits to several kilobits of data can be recorded in a memory of the IC chip, and a sufficient amount of the information can be recorded as the information on each of the articles or the like. Furthermore, communication can be performed with a reading/writing device side in a non-contact manner, and hence there is no fear of wear, damage, dirt or the like on a contact. Additionally, the tag itself can include no power source, and hence processing, miniaturization and thinning of the tag can be performed in compliance with each object.
Furthermore, by use of such an RF tag, it is possible to record various pieces of information on each article to which the tag is attached, e.g., a name, an identification symbol, a content, components, a manager, a user, a use state, a use situation and a date of the article. Therefore, a large variety of pieces of information, which are impossible by characters, a bar code or the like printed and displayed on the surface of a label, can correctly be read and written simply by attaching the miniaturized and thinned tag to the article.
However, when this RF tag is attached to, e.g., each of plastic bottles and glass bottles to be charged with liquids and the like and then used, the tag is easily influenced by the content (water) in each container. Furthermore, when the tag is attached to each of containers and articles made of a metal, e.g., can containers and pouch containers, the tag is disadvantageously influenced by a conductivity of the metal. Thus, a communication distance to changes or a radio communication cannot correctly be performed. Therefore, when the usual RF tag for general purpose is attached to each of the containers for beverages and the articles made of the metal as it is, the tag wrongly operates or the radio communication with the reader/writer cannot be performed.
Particularly, in the RF tag of a radio wave system using a high frequency band of a UHF band, as compared with a tag of an electromagnetic induction system using a 135 KHz or 13.56 MHz zone, the communication distance lengthens, but communication characteristics are noticeably impaired due to absorption of water, reflection by the metal or the like.
Further, for example, in Japan, a frequency band of the RF tag has been shifted from a heretofore used 950 MHz band (950 to 958 MHz: an 8 MHz width) of the UHF band to a 920 MHz band (915 to 930 MHz: a 15 MHz width) by the revision of the Radio Wave Law, and hence a utilizable frequency band has been enlarged.
Also in the RF tag using the 920 MHz band after the above shift, the abovementioned influence of the metal is not avoidable, and it is strongly desired that effective measures are taken.
Here, as means for improving communication characteristics in the RF tag, it has been suggested that an antenna disposed in the RF tag is constituted of a planar patch antenna (e.g., see Patent Documents 1 and 2).
The communication characteristics of the RF tag depend on a gain due to an antenna size. Therefore, when the antenna disposed in the RF tag is formed into the planar shape to increase the antenna size, a large communication distance is acquired to enable improvement of the communication characteristics.